NEW YORK (CNNMoney.com) -- For many years, the Internet was relatively simple: Everyone surfed the same Web.

Fast forward to 2010 and the idea of a one-size-fits-all Web is a quaint memory, thanks to the rise of the iPhone, Kindle, BlackBerry, Droid and of course, the much-hyped iPad.

As mobile Internet gadgets multiply, so does device-specific content. For example, popular mobile Twitter app Tweetie is available only on the iPhone, while the GMail application is only on the Droid. And if you buy an e-book for the Amazon Kindle, you can't read it on your Apple iPad.

At the same time, more and more online content is password-protected, like most Facebook profiles and some newspaper articles.

It's a tangled Web they're weaving. Simply put, the Internet we once knew is shattering into pieces. It's the end of a golden age, according to Forrester Research analyst Josh Bernoff, who recently coined the term "splinternet" to describe this phenomenon.

"It reminds me of the early Internet provider battles with AOL and CompuServe," said Don More, a partner at Internet research firm Updata. "There are going to be winners and losers."

In those early days of the Web, users viewed content using those specific systems; that is, AOL users saw only AOL content. Then the World Wide Web became an open platform. Now, mobile devices are splitting up the Web again.

"You can't put Humpty Dumpty back together again," Bernoff said. "The stability that helped shape the Web is gone, and it's not coming back."

When mobile users choose to buy an iPhone, Motorola Droid, BlackBerry or some other device, they are effectively opting into and out of certain content, since not every application is available on every gadget.

This is putting content into "gated communities," said Updata's Dan More. The manufacturers of these devices can -- and do -- pick and choose which apps their devices will work with, rejecting those that may compete with their own products or that they don't consider up to snuff.

For example, Apple rejected a Google Voice app for the iPhone, which would have let users send free text messages and make international calls at a low cost.

And limitations extend further than just the apps. Case in point: The new iPad does not run Adobe's Flash, which will prevent users from viewing a lot of Web sites.

"While [this trend] is not necessarily bad for consumers, they should realize that they are now making a choice," said Forrester's Bernoff. "Whatever they choose, some content will not be available to them."

The companies that make the apps are now faced with difficult decisions. Which devices will they choose to support? How much money and time will it take to get their content to run on these gadgets?

Whatever developers decide, they'll miss some portion of the consumer population that they were once able to reach on the Web as a whole.

"When we started this business, we never dreamed of what we'd have to deal with," said Sam Yagan, co-founder of dating site OKCupid.com. "To rewrite a program for a different phone is time-consuming, expensive and mind-numbing."

OkCupid employs 14 people, and its iPhone app took six months of man-hours to develop, Yagan said. The company is considering creating an app for Android, which would take about two months.

"It's a huge resource allocation problem, especially for smaller companies," Yagan said. "We just don't have the resources to throw five people on every device that comes out."

Chris Fagan, co-founder of comparison shopping app maker Froogloid, said his company chose to focus on Android because it works with several phones including the Droid, Eris and G1.

"Consumers are losing some of that choice, and businesses are being hurt by the extra cost," Fagan said. But the burgeoning popularity of apps means that companies will continue building them despite the cost, he said.

As a more splintered Internet becomes the norm, Bernoff of Forrester thinks there will be a backlash: a push to make content on mobile devices more uniform.

The answer might be the newest Web platform coming down the pike, HTML 5, which Bernoff said could become a standard for mobile devices in the next few years. For example, HTML 5 can showcase Web site animation without using Flash.

But the arrival of any new technology also sets off a fight to control it. Don More of Updata said he expects to see "a massive battle among companies -- not just Apple and Google, but also Comcast, Disney and anyone else who touches content. There's the apps, the ads, the devices ... everyone is trying to control this emerging technology."

Of course, no one can predict the future of the Web. But Bernoff knows one thing for sure.

"We don't know what the hot new device will be in 2011," he said. "But this is certain: It's not going to run the Internet the same way we once knew."

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